In electrohydraulic systems that include a plurality of electrohydraulic devices, such as actuators, motors and pumps, it has heretofore been proposed to couple each of such devices to an associated device controller, and to connect all of the device controllers to a remote central or master controller for coordinating device operation to perform desired tasks. Motors and actuators may be employed, for example, at several coordinated stages of a machine tool line for automated transfer and machining of parts at a series of work stations. In another typical application, the moving components of an earth excavator may be coupled to electrohydraulic actuators and motors controlled by a master controller responsive to operator lever or joystick inputs.
U.S. Pat. Nos. 4,744,218 and 4,811,561, both assigned to the assignee hereof, disclose distributed control systems that include a plurality of device controllers each dedicated to operation of an associated actuator or pump, and a central or master controller connected to the device controllers by a high-speed bidirectional serial data bus. Internal programming within the master controller establishes a repetitive time sequence of windows for communication in turn with the various device controllers for downloading control signals and parameters, and for uploading data indicative of system status and operation. The various device controllers include internal programming for operating the associated electrohydraulic devices as a function of control signals and parameters received from the master controller. U.S. Pat. Nos. 4,745,744 and 4,757,747, also assigned to the assignee hereof, disclose suitable master and device controller constructions respectively. U.S. application Ser. No. 07/412,211, filed Sep. 25, 1989, now U.S. Pat. No. 5,073,091 likewise assigned to the assignee hereof, discloses a controller suitable for use in association with a hydraulic pump.
Although the overall system and various controllers disclosed in the noted patents and application represent a significant advance in the electrohydraulic system control art, further improvements remain desirable. Specifically, there is a need for a universal controller construction that may be selectively employed as either a master controller or a device controller dedicated to operation of one or more specific electrohydraulic devices, that will provide enhanced flexibility in system design, that will simplify maintenance and repair, and that will reduce manufacturing and inventory costs. A general object of the present invention is to provide such a universal controller construction.